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Manure Spreading and Its Effects on Soil Compaction and Corn Yield in Southern Wisconsin Gregg Sanford 1,Joshua Posner 1,Janet Hedtcke 1,Ron Schuler 2, and Jon Baldock 3 1 Department of Agronomy, The University of Wisconsin-Madison 2 Department of Biological Systems Engineering, The University of Wisconsin-Madsion 3 AgStat, Verona, Wisconsin Introduction Interviews with grain farmers have indicated that the fear of compaction from manure spreading equipment is one factor that limits the land they are willing to make available for applying livestock waste. Their concerns are not unfounded as manure slurry tankers commonly range from 11 to 26 m 3 (3,000 to 7,500 gallon) capacity and can weigh from 9 to 20 Mg (10 to 22 tons) per axle. Axle weights greater than 9 Mg have been shown to contribute to subsoil compaction that is generally not alleviated by freeze/thaw cycles or tillage (Håkansson et al., 1987, Lowery and Schuler, 1991, 1994). Protocols were developed to address three questions: 1) Does normal tanker traffic cause soil compaction?; 2) If so, does this compaction affect whole plot yields?; and 3) If yields are depressed, do the soil building and fertility effects of manure offset the effects of compaction? Methods and Materials On-Farm Trials Corn Yields Eight on-farm sites were set up in the fall of 2004 and six in 2005. At each site three treatments were compared (manure (M), farmer’s check w/o manure (F), and loaded tanker traffic only (C)), and replicated three times. Plots were typically 9m (30ft) wide and 91m (300ft) long. Dairy slurry was spread primarily in the fall following soybean or wheat harvest. Typical axel weights of the full slurry tankers were 9 to 14 Mg (10 – 15.5 tons). All trials were planted to corn during the 2005 and 2006 growing seasons. Whole plot yields were taken in the fall of each season. Penetrometer Penetrometer readings were taken in the spring before corn plants reached the V6 stage. In each plot two randomly placed sampling transects were defined. Each transect began in the middle of the plot and extended to the plot edge, with penetrometer readings taken every 0.3 m (1 ft). A data logging hand held penetrometer was used that recorded applied pressure in pounds per square inch (psi) at 2.54 cm (1 in) increments to a depth of 46 cm (18 in). Data from each plot was then assigned to one of three groups (1-3) for analysis. Group 2 consisted of the middle 3.6 m (12 ft) of each plot (approximate area of tanker traffic), and groups 1 and 3 consisted of the outer 3 m (10 ft) of each plot. Headlands Study Corn Yields At an additional site, the impact of multiple passes of slurry equipment was examined (axel weight 10.8 Mg). This experiment was set up as an augmented 2 by 2 factorial with two levels of traffic (1 or 6 passes with a loaded tanker), two nitrogen sources (manure or commercial fertilizer), and a no manure no tanker check. Treatments were: check plot (F), compaction-only 1-pass (C1), compaction with 6-passes (C6), dairy slurry 1-pass (M1) and dairy slurry 6-passes (M6) In this case manure was spring applied and plots were 9 m (30 ft) by 46 m (150 ft). Tire tracks were clearly marked following manure application. Three random sampling stations were set up in each plot. Stations were 1.5 m wide (3 corn rows) with a row in the track and the two successive rows. Prior to whole plot harvests in the fall 1.5 m lengths of each corn row at the stations was hand- harvested. Penetrometer Penetrometer readings were taken in each sampling station at 38 cm (15 in) increments starting in the tire track. This resulted in 5 readings per station. Results On-Farm Trials Median penetrometer values from 10 to 25 cm (4 – 10 in.) were used to compare treatments and groups. Analysis of these points indicated a highly significant group effect (p <0.0001) and a strong treatment by group effect (p = 0.058). Group 2 (center of the plot) for treatments C and M showed significantly greater compaction (α = 0.1) than group 2 for the check plot (F) (Fig. 1). Somewhat surprisingly, despite significantly greater penetrometer readings in the manured (M) and compacted plots (C), there were no significant whole plot yield differences overall (mean 11.8 Mg ha-1 (191 bu/a)). Headlands Study Median penetrometer readings showed significant differences (α = 0.05) between points within a treatment from 10 to 25 cm (4-10 in) depth, with attenuation of psi readings from point 1 (in-track) to point 5 (152cm from track). The two six-pass treatments showed significantly greater levels of compaction than the one-pass and check treatments in 2006 (Fig. 3). In 2005, only the 6 passes treatment without manure was significantly higher in the same depth range than the other 4 treatments in 2005. Stunted plants and reduced yields (only 80% of the more distant rows) were found on the in-track row of corn (C6 & M6) that was hand harvested (Fig. 2, Table 1). Whole plot yields however, again showed no significant difference between treatments with an overall mean of 12.17 Mg ha-1 (194 bu/a) in 2005. Conclusions 1. Traffic from loaded slurry tankers did result in significantly greater soil compaction compared to check plots. 2. Tanker traffic, with or without manure application, did not significantly affect whole plot yields in the on farm trials nor the headlands trial, despite visible stunting in tire-track row in the 6-pass traffic treatments (C6 and M6). References Håkansson, I., Voorhees, W.B., and Riley, H., 1987. Vehicle and wheel factors influencing soil compaction and crop response in different traffic regimes. Soil & Tillage Research. 11: 239-282. Lowery, B., and Schuler, R.T. 1991. Temporal effects of subsoil compaction on soil strength and plant growth. Soil Sci. Soc. Am. J. 55: 216-223. Lowery, B., and Schuler, R.T. 1994. Duration and effects of compaction on soil and plant growth in Wisconsin. Soil & Tillage Research. 29: 205-210. Fig 3: Median penetrometer readings: check plot (F), compaction-only 6 pass (C6) and compaction only 1 pass (C1). Distances from track (1-5) in 38cm (15 in) increments, 1 = in- track. 2006 data. F C6 * Letters indicate significance at, α = 0.1. a a bcd bc b bcd cd d C1 median psi Fig 2: Stunted plants in rows affected by six passes of loaded slurry tanker (C6). median psi Table 1: Hand-harvest Yields (kg m -2 ) Trt. In- Track Corn 2 nd Corn Row 3 rd Corn Row F1.11ab1.20a1.18a C11.10ab1.17ab1.18a C60.92b1.10ab1.23a *Yields with different letters indicate significance at α=0.1. 68DAP compaction-onlyfarmers checkmanure Fig 1: on-farm penetrometer results